The present invention relates to a cryostat, in particular for superconductive magnets, comprising different components nested in each other, one of them forming an outer shell and at least another one forming a tank arranged in the latter for receiving a coolant, and comprising further tension means for interconnecting each inner component with its respective adjacent outer component, the said tension means containing glass fibers or aramide fibers and being equipped at their ends with tie rods by means of which they are fixed to the respective component, the ends of the tension means consisting of glass fibers or aramide fibers and being fixed in a conical bore arranged in the tie rod. Further, the invention relates to a method for producing tension means of this kind.
In the case of cryostats for superconductive magnets of the general structure described before, particular problems are encountered in connection with the construction of the tension means which normally are designed as tension bars. Such tension bars must exhibit high tensile strength, in order to be able to safely carry the relatively important masses, and at the same time low thermal conductivity in order to keep the heat transmission to the interior of the cryostat as low as possible. Further, they should be easy to produce and to assemble and require a minimum of space in the cryostat because the spaces required for accommodating them may considerably increase the overall volume of such a cryostat.
There have been known plastic rods (WO 86/04016) which are reinforced by directional glass fibers. Such tension bars provide the advantage that they offer the required tensile strength without, however, requiring too much space in the cryostat. The ends of such tension bars are provided with tie rods through which the forces are introduced. An intimate connection between the tension bar and the tie rod is achieved by the fact that the glass fibers are formed to a loop at the end of the plastic rod and that the loop projects from the end of the plastic bar. The tie rod is provided with a conically widening bore, and the end of the tension bar is passed through such bore in such a manner that the glass fiber loop projects beyond the wider end of the bore. Now, a wedge is introduced into the projecting loop, the glass fibers and the wedge enclosed by them are pulled into the bore, which gets narrower in the direction of tension, and the glass fibers are finally cured in this position.
This high-strength connection between the tie rod and the tension bar is connected, however, with the disadvantage that the ends of the tension bars must be provided with glass-fiber loops which not only is rather cost-intensive, but requires in addition considerable input as a plurality of tension bars of different lengths are used in a cryostat so that a special tension bar with the described loops formed on its ends has to be produced for every such length. The different materials of the tie rod, the wedge and the plastic rod create the additional disadvantage that due to the different coefficients of expansion it is not possible to achieve a reliable surface bond between the tension bar and the tie rod so that this connection offers only limited security from failure.